Charge coupled devices (CCD's) of the type disclosed in Sequin et al, Charge Transfer Devices, Academic Press, 1975 have a limited density of CCD charge packet storage cells or "buckets" within a given area. This has limited the performance of charge coupled image sensors such as those disclosed in the above-referenced Sequin publication at pages 142-200. Charge coupled image sensors using time delay and integration (TDI) are disclosed by Erb et al, "Buried Channel Charge Coupled Devices for Infrared Applications," CCD Aplications Conference, Proceedings, Sept. 18-20, 1973, San Diego, Calif. In such devices a field of view is scanned by a column of image detectors in synchronism with charge transfer in an adjacent output CCD serial register and the charge transfer in the CCD register occurs at the same rate that the adjacent detectors are scanned across the field of view. Accordingly, the sampling rate, or the number of samples taken within a given area of the field of view, is limited by the density of buckets in the CCD serial register. Although the number of samples may be increased by crowding the image detectors together and increasing the density of the charge coupled device bits, such miniaturization has the effect of limiting the charge capacity of each bucket of the charge coupled device register, thus limiting the dynamic range of the image sensor. Thus, in time delay and integration (TDI) charge coupled device (CCD) imagers, a trade-off exists between sampling rate and dynamic range. Accordingly, it has not seemed possible in the prior art to maximize dynamic range while at the same time maximizing the sampling rate.
It has been a general goal in the prior art to find ways to increase the linear density of charge coupled device cells or buckets without having to reduce the CCD geometry or dynamic range. One advance made in the prior art is the meander channel CCD which is useful for both charge coupled device image sensors and for charge coupled device signal processors. The meander channel CCD, instead of moving charge in a straight line, causes the charge to be transferred in meandering fashion along a serial register which has the appearance of two parallel linear serial registers. One such device particularly useful with TDI CCD imagers, is disclosed in U.S. Pat. No. 4,380,056 issue Apr. 12, 1983, filed Feb. 20, 1981 by William J. Parrish and Christopher L. Fletcher and entitled "Charge Coupled Device Focal Plane with Serial Register Having Interdigitated Electrodes," and assigned to the assignee of the present application, the disclosure of which is incorporated herein by reference.
The main advantage of meander channel CCD's is that their production yield is generally greater than that of the usual linear CCD's.